Conventionally, truck tractors have been coupled to a semi-trailer by a coupling device commonly referred to as a "fifth wheel". Accordingly, the truck tractor has a "fifth wheel" comprising a substantially round flat plate positioned in a substantially horizontal plane to form a tractor bearing surface. The semi-trailer includes a king pin extending downwardly to locate and seat within a slot in the fifth wheel of the tractor. The trailer further includes a trailer bearing surface to match the tractor bearing surface. Once coupled, the tractor and trailer can pivot about the king pin to permit the truck and trailer to articulate when turning. Because the tractor bearing plate necessarily bears a large portion of the trailer weight, much friction between the two bearing surfaces is developed. This friction adversely affects handling, increases tire wear, fatigues the driver, and causes damage and structural cracks to crossmembers, frame rails and to the suspension systems.
In order to reduce this friction, a lubricant such as grease has been placed between the truck tractor and semi-trailer bearing surfaces. However, it is difficult to maintain a satisfactory layer of grease between the two bearing surfaces, thus requiring the grease to be often replenished. In addition, grease is very messy, attracts dirt and falls from the tractor to the road surface, thus becoming a hazard to vehicles. Further, as the grease dissipates, the handling and performance characteristics of the truck tractor and semi-trailer deteriorate such that oversteer is experienced.
As one way to eliminate the need for a layer of grease, bearings, ball or roller, have been utilized to permit the tractor bearing surface itself to rotate. However such coupling devices are relatively complex, expensive, heavy and difficult to maintain.
Still others have replaced the layer of grease with a substrate having a low coefficient of friction, such as Teflon.RTM. or various plastics, secured as a cover to the tractor bearing surface. Such covers are disclosed in U.S. Pat. No. 4,542,912 to St. Louis and U.S. Pat. No. 4,169,635 to Szalay. However, these covers are unprotected and are still subject to wear. Further, upon accumulating road dirt or thin surfaces, these covers become ineffective.
Additionally, when pulling an empty trailer, especially one of today's lightweight aluminum trailers, the trailer bearing surface tends to bounce on the tractor bearing surface. This vibration is transmitted into the tractor cab, further adding to the fatigue and discomfort of the driver. Likewise, metal fatigue to the truck tractor and semi-trailer increases.
The present invention is provided to solve these and other problems.